This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the presently described embodiments. This discussion is believed to be helpful in providing background information to facilitate a better understanding of the present embodiments. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
The present disclosure generally relates to a system and methods for fracturing subterranean formations, and more specifically, to a system and methods for breaking friction reducers in subterranean formations in-situ during hydraulic fracturing operations.
It is common practice to treat a subterranean formation to increase the permeability or conductivity of the formation. These procedures are identified generally as fracturing operations. For example, it is a conventional practice to hydraulically fracture a well in order to produce one or more cracks or “fractures” in the surrounding formation by mechanical breakdown of the formation.
Hydraulic fracturing may be carried out in wells which are completed in subterranean formations for virtually any purpose. The usual candidates for hydraulic fracturing, or other stimulation procedures, are production wells completed in oil and/or gas containing formations. However, injection wells used in secondary or tertiary recovery operations, for example, for the injection of water or gas, may also be fractured in order to facilitate the injection of fluids into such subterranean formations.
Hydraulic fracturing is accomplished by injecting a fracturing fluid into the well and applying sufficient pressure on the fracturing fluid to cause the formation to break down with the attendant production of one or more fractures. The fracture or fractures may be horizontal or vertical, with the latter usually predominating, and with the tendency toward vertical fracture orientation increasing with the depth of the formation being fractured. Typically, the primary component of a fracturing fluid is water. In addition to water, a fracturing fluid can contain one or more additives to facilitate formation fracturing.
Usually a gel, an emulsion, or a foam, having a proppant such as sand or other particulate material suspended therein, is carried in the fracturing fluid and introduced into the fracture. The proppant is deposited in the fracture and functions to hold the fracture open after the pressure is released and the fracturing fluid flows back into the well. The fracturing fluid has a sufficiently high viscosity to retain the proppant in suspension or at least to reduce the tendency of the proppant to settle out of the fracturing fluid as the fracturing fluid flows along the created fracture. Generally, a gelation agent and/or an emulsifier is used to gel or emulsify the fracturing fluid to provide the high viscosity needed to realize the maximum benefits from the fracturing process.
Practical and cost considerations for hydraulic fracturing operations require the use of additives to reduce the required pumping pressure. This can be accomplished by introducing additives that reduce the frictional drag of the fracturing fluid against the well tubulars, which serve as a conduit for the fluid into the formation. High-molecular weight, long-polymer chain polymers are widely used as friction reducing additives, or “friction reducers,” to this end. Non-limiting examples of such polymers are polyacrylamide-based polymers. The long chain, high molecular weight polymers work by reducing the turbulent flow regime in the fracturing fluid into laminar flow. Laminar flow results in lower frictional drag and pressure buildup compared to turbulent flow. In this way, these polymers reduce turbulence and backpressure from friction within the well tubulars, thereby reducing pressure pump power demands.
Other, non-limiting, categories of fracturing fluid additives include biocides to prevent microorganism growth and to reduce biofouling of the fractures, corrosion inhibitors to prevent corrosion of metal pipes, scale inhibitors to prevent mineral scale formation as the fracturing fluid mixes with formation water or after dissolving existing mineral salts in the reservoir, acids to remove drilling mud damage within the near-wellbore area, crosslinking agents to increase fluid viscosity to deliver proppant into the formation, surfactants to reduce interfacial tension in the subterranean formation and to promote more robust water recovery after hydraulic fracturing, and the like. Any other additives well-known in the art and suitable for well treatment purposes are also envisioned.
When using friction reducers in hydraulic fracturing operations, the friction reducers tend to easily adsorb onto the subterranean formation. This can present a number of challenges. For instance, the friction reducer may actually plug some of the subterranean formation pore spaces, thereby decreasing formation conductivity. Further, the friction reducer may hinder recovery of the fluid used in the hydraulic fracturing operations. In addition, the friction reducer can provide a source of nitrogen that may support the growth of bacteria in the formation. Friction reducer that is not adsorbed, but that remains in solution in recovered water, will also make disposal of that water more difficult once the water is retrieved to the surface.
Accordingly, it is advantageous to break the friction reducer (e.g., by breaking the polymer backbone) so that the friction reducer can be substantially cleaned from the subterranean formation and returned to the surface. Compositions used in this process to interact with the friction reducer may be referred to in the art as “breakers.”
Generally, breakers and friction reducers are pumped down the wellbore at the same trip. The most commonly used breakers for friction reducers are in solid form and the solid breakers need to be well dispersed in the fracturing fluid in order to breakdown the friction reducers completely. However, in most cases this is challenging due to the concentration gradient of the breakers and the requirement that the breakers must be uniformly distributed in the fracturing fluid. Adding breakers into the fracturing fluid is a “two-stream” process. Because more the one chemical is being added, another pipeline must be used in the process so that the two chemicals may be pumped and mixed well. The additional pipeline and mixing requires higher cost and a more complex operation.
Accordingly, a system and method for breaking friction reducers during hydraulic fracturing operations which reduces surface operation complexity and increases formation permeability and conductivity is desired.
The illustrated FIGURE is only exemplary and is not intended to assert or imply any limitation with regard to the environment, design, or process in which different embodiments may be implemented.